In case where more than one telephone set, facsimile machine or other telephone-line utilization apparatus is connected to the same telephone-line, it is desired that, when a specified one of these telephone-line utilization apparatus is operated, for example a telephone set of these telephone-line utilization apparatus is "on-hooked" (its telephone receiver is taken off for a phone call), all of the other telephone-line utilization apparatuses are caused to be in a "dead" condition to be unable to be used. This is important in that the privacy of the specified telephone set is kept from the other telephone sets connected to the same telephone-line. Further, if the specified telephone-line utilization apparatus is a facsimile machine, this is protected against a noise which is inadvertently generated by the other equipments connected to the same telephone-line.